Getting up to speed with neutron therapy

Advances in particle physics have significantly contributed to medical science over the past century, providing techniques such as magnetic resonance imaging, laser eye surgery, and radiotherapy. More recently, researchers have been developing new tools in the battle against cancer – beams of neutrons, which might act as safe and effective treatments for the most aggressive tumours.

At the Budker Institute of Nuclear Physics in Siberia, Sergey Taskaev and co-workers have developed a reliable source that produces so-called epithermal neutrons (energies between 0.4 eV and 10 keV), which have relatively slow speeds up to around 1 million m/s, and are suitable for boron neutron capture therapy (BNCT). This technique involves injecting a malignant tumour with non-radioactive boron, then bombarding the site with the neutrons, triggering the release of high-energy alpha particles, comprising two protons and two neutrons, that kill the cells.

Now, the team have adapted their accelerator to produce higher energy (up to 20 million eV) ‘fast neutrons’, which travel up to 60 million m/s and can kill cancer by attacking the tumour cell nuclei. Taskaev is excited about the team’s research, and what’s coming next.

“The idea to make a neutron source for BNCT was born in 1998. The main idea was to do what we needed to do, not what we knew how to do,” he laughs. “BNCT requires epithermal neutrons, and they are best obtained by irradiating a lithium target with a low energy, high current proton beam. But at that time, there was no suitable proton accelerator or lithium target.”

This meant that the team had to invent and build their own accelerator and target. Their facility now produces a whole range of particles including protons, deuterons, neutrons, photons, alpha particles, and positrons. Their findings and ideas for implementing BNCT have been realized in a commercial product which should start being used to treat patients this year at a clinic in Xiamen, China.

According to Taskaev, the technical changes required to produce faster neutrons were quite simple. “All we did was replace a cylinder of hydrogen in the ion source with a cylinder of deuterium,” he says. “The accelerator is equipped with such a wide range of diagnostic tools that we could quickly select a new mode to obtain deuterons.”

As well as promising novel cancer treatments, the neutron beams can be used to detect explosives and drugs, or for quality-testing materials, as Taskaev explains:

“We recently irradiated samples of boron carbide and steel to select the best parts to use in ITER – the world’s largest fusion reactor experiment. Soon we will bombard the fibre samples with fast neutrons to determine their resistance to such irradiation.”